This invention concerns polyurea elastomers prepared from aspartic esters, and processes for the preparation thereof.
Polyurea elastomers have previously been made using primary amines as reactants. One common problem with such systems is the high reactivity of the polymerization reaction. As a result, it is difficult to obtain smooth finishes in coatings made from the polyurea elastomers. To decrease the reactivity of the system, it has been previously proposed to employ secondary amines as the amine component of the system. One such secondary amine that has been proposed is polyaspartic ester, which is derived from a primary polyamine and diethyl maleate, for example. The polyaspartic ester derived polyureas have a number of advantageous properties, such as smooth, glossy film surface, excellent elongation (high) at a high elastomer strength, excellent ultraviolet color stability, good low temperature property retention and flexibility, slow reactivity for ease of processing and substrate wet-out (improved adhesion). Use of the polyaspartic esters, however, results in slow polymerization reaction. A polyaspartic ester system has proven to be too slow for rapid coating applications. Hence, these systems heretofore required catalysts such as organo tin compounds to increase the reactivity to acceptable levels. However, the catalysts increase cost of such polyureas, increase the complexity of the polyurea manufacturing process. In addition, use of catalysts lead to poor component stability over extended periods, increased moisture sensitivity in the system, overall system reactivity being affected by changes in environmental and substrate temperature, and polymer breakdown under stressful conditions that do not normally affect polyurea systems (i.e., high heat/humidity, UV light).